DNA sequences encoding phospholipase A2 enzyme and processes for producing enzyme

ABSTRACT

The invention provides novel DNA and peptide sequences encoding a family of phospholipase A 2  enzymes, with specific activities of approximately 20 μmol/min/mg in the mixed micelle assay. These enzymes are useful in methods for detecting the anti-inflammatory potential of various chemical agents. The invention also details novel methods for determining such potential using the novel sequences, methods for making the novel peptides, and methods for developing new anti-inflammatory drugs.

This is a division application of U.S. patent application Ser. No.486,628 filed Feb. 28, 1990.

The present invention relates to novel DNA and peptide sequencesencoding a family of phospholipase A₂ enzymes, which are useful inmethods for detecting the anti-inflammatory potential of variouschemical agents. The invention also details methods for making the novelpeptides, and methods for developing new anti-inflammatory drugs.

BACKGROUND OF THE INVENTION

Leukotrienes and prostaglandins are important mediators of inflammation.Leukotrienes recruit inflammatory cells such as neutrophils to aninflamed site, promote the extravasation of these cells and stimulaterelease of superoxide and proteases which damage the tissue.Leukotrienes also play a pathophysiological role in the hypersensitivityexperienced by asthmatics [See, e.g. B. Samuelson et al., Science,237:1171-76 (1987)]. Prostaglandins enhance inflammation by increasingblood flow and therefore infiltration of leukocytes to inflamed sites.Prostaglandins also potentiate the pain response induced by stimuli.prostaglandins and leukotrienes are unstable and are not stored incells, but are instead synthesized [W. L. Smith, Biochem. J.,259:315-324 (1989) from arachidonic acid in response to stimuli.Likewise arachidonic acid is not free in cells but is released from thesn-2 position of membrane phospholipids by Phospholipase A2 (hereinafterPLA₂). The reaction catalyzed by PLA₂ is believed to represent therate-limiting step in the process of lipid mediator biosynthesis. Whenthe phospholipid substrate of PLA₂ is of the phosphatidyl choline classwith an ether linkage in the sn-1 position, the lysophospholipidproduced is the immediate precursor of platelet activating factor(hereafter called PAF), another potent mediator of inflammation [S. I.Wasserman, Hospital practice, 15:49-58 (1988)]. Consequently the directinhibition of the activity of PLA₂ has been suggested as a usefulmechanism for a therapeutic agent, i.e., to interfere with theinflammatory response. [See, e.g., J. Chang et al, Biochem. Pharmacol.,36:2429-2436 (1987)].

A family of PLA₂ enzymes characterized by the presence of a secretionsignal sequenced and ultimately secreted from the cell have beensequenced and structurally defined. These secreted PLA₂ 's areapproximately 14 kD molecular weight and contain seven disulfide bondswhich are necessary for activity. These PLA₂ s are found in largequantities in mammalian pancreas, bee venom, and various snake venom.[See, e.g., references 13-15 in Chang et al, cited above; and E. A.Dennis, Drug Devel. Res., 10:205-220 (1987).]However, the pancreaticenzyme is believed to serve a digestive function and, as such, shouldnot be important in the production of the inflammatory mediators whoseproduction must be tightly regulated.

Recently, the primary structure of the first human non-pancreatic PLA₂has been determined. This non-pancreatic PLA₂ is found in platelets,synovial fluid, and spleen and is also a secreted enzyme. This enzyme isa member of the aforementioned family. [See, J. J. Seilhamer et al, J.Biol. Chem., 264:5335-5338 (1989); R. M. Kramer et al, J. Biol. Chem.,264:5768-5775 (1989); and A. Kando et al, Biochem. Biophys. Res. Comm.,163:42-48 (1989)].

However, it is doubtful that this enzyme is important in the synthesisof prostaglandins, leukotrienes and PAF, since the non-pancreatic PLA₂is an extracellular protein which would be difficult to regulate, andthe next enzymes in the biosynthetic pathways for these compounds areintracellular proteins. Moreover, there is evidence that PLA₂ isregulated by protein kinase C and G proteins [R. Burch and J. Axelrod,Proc. Natl. Acad. Sci. U.S.A., 84:6374-6378 (1989)] which are cytosolicproteins which must act on intracellular proteins. It would beimpossible for the non-pancreatic PLA2 to function in the cytosol, sincethe high reduction potential would reduce the disulfide bonds andinactivate the enzyme.

A murine PLA₂ has recently been identified in the murine macrophage cellline, designated RAW 264.7. A specific activity of 2 μmols/min/mg,resistant to reducing conditions, was reported to be associated with theapproximately 60 kD molecule. However, this protein was not purified tohomogeneity. [See, C. C. Leslie et al, Biochem. Biophys. Acta.,963:476-492 (1988)]. The references cited above are incorporated byreference herein for information pertaining to the function of thephospholipase enzymes, particularly PLA₂.

There remains a need in the art for a definitive identification of anintracellular PLA₂ enzyme, purified from its natural source or otherwiseproduced in purified form, which functions intracellularly to producearachidonic acid in response to inflammatory stimuli. Such enzymes maybe useful in methods for developing effective anti-inflammatory agentsfor therapeutic use in a variety of disease states.

BRIEF SUMMARY OF THE INVENTION

In one aspect the present invention provides a first well-definedintracellular and biologically active mammalian PLA₂ enzyme which issubstantially free from association with other mammalian proteins. Anovel human biologically active enzyme is characterized by containingall or a portion of the same or substantially the same amino acidsequence reported below in Table I. Alternatively, DNA sequences capableof hybridizing to the sequence of Table I may encode the enzyme.

In another aspect, there is disclosed a second novel mammalianbiologically active PLA₂ enzyme characterized by containing all or aportion of the same or substantially the same amino acid sequencereported below in Table II. The partial DNA sequence encoding this novelenzyme is reported in Table II. Alternatively, DNA sequences capable ofhybridizing to the sequence of Table II may encode the enzyme.

The mammalian PLA₂ enzymes of this invention are further characterizedby each having an apparent molecular weight of approximately 110 kD asdetermined by sodium dodecyl sulfate polyacrylamide gel electrophoresisunder reducing conditions. These enzymes are further characterized byresistance to dithiothreitol, indicating that little to no disulfidebonds exist in the structures of the active homogenous enzymes.

The PLA₂ enzymes of this invention have displayed enzymatic activity inthe mixed micelle assay, with a specific activity of 20 μmols/min/mgassociated with the 110 kD protein. This activity is not affected byincubation with disulfide reducing agents. The activity indicates thefunction of the homogenous enzymes of this invention as cytosolicphospholipase enzymes, involved in regulating the prostaglandin andleukotriene pathways, as well as the biosynthesis of platelet activatingfactor (PAF).

Another aspect of the invention includes novel DNA sequence coding onexpression for a mammalian PLA₂ enzyme. The enzyme may be encoded by theDNA sequence reported in Table I, a fragment thereof or a sequencecapable of hybridizing thereto. The enzyme may be encoded by the DNAsequence reported in Table II, a fragment thereof or a sequence capableof hybridizing thereto.

Also provided by the present invention are vectors containing a DNAsequence encoding a mammalian PLA₂ enzyme in operative association withan expression control sequence. Host cells transformed with such vectorsfor use in producing recombinant PLA₂ are also provided by the presentinvention.

The vectors and transformed cells of the invention are employed inanother aspect, a novel process for producing recombinant mammalian PLA₂enzyme. In this process a cell line transformed with a DNA sequenceencoding on expression for PLA₂ enzyme in operative association with anexpression control sequence therefore is cultured. This claimed processmay employ a number of known cells as host cells for expression of thepolypeptide. Presently preferred cell lines are mammalian cell lines,insect cells and bacterial cells.

Another aspect of this invention provides methods for identifyinganti-inflammatory compounds by determining if a selected compound iscapable of inhibiting the action of PLA₂ in cleaving a phospholipid torelease fatty acids in a mixed micelle assay, a liposomc assay, a systemutilizing natural membranes, or in whole cells overexpressing thisenzyme. A compound capable of inhibiting this PLA₂ activity isindicative of use as an anti-inflammatory compound.

Still another aspect of this invention is an anti-inflammatory compoundfirst identified by the method described above as inhibiting theactivity of PLA₂ of this invention. Novel pharmaceutical compositionsmay contain a therapeutically effective amount of a compound identifiedby a method of this invention. These pharmaceutical compositions may beemployed in methods for treating disease states or disorders mediated bymetabolites of arachidonic acid or PAF, e.g., asthma, rheumatoidarthritis and the like.

A further aspect of the invention, therefore, is a method for treatingdisorders, diseases, tissue injuries and diseases characterized by aninflammatory reaction by administering to a patient a therapeuticallyeffective amount of a compound first identified by the method of thepresent invention in a suitable pharmaceutical carrier.

Still another aspect of the present invention are antibodies directedagainst the PLA₂ enzymes of this invention. Anti-PLA₂ antibodies may beemployed as diagnostic or research agents for use in further exploringand possibly treating inflammatory responses. PG,11

Other aspects and advantages of the present invention will be apparentupon consideration of the following detailed description of preferredembodiments thereof.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides novel biologically active mammalian PLA₂enzymes, substantially free of association with other mammalianproteinaceous materials. These proteins may be produced in a variety ofways, including via recombinant DNA techniques to enable large scaleproduction of pure, active PLA₂ useful for screening compounds foranti-inflammatory therapeutic applications, and developing antibodiesfor therapeutic, diagnostic and research use.

Human PLA₂ was originally purified from the human monocytic cell lineU937, available from the American Type Culture Collection, 12301Parklawn Drive, Rockville, Md. (ATCC) under accession number ATCC CRL1593. The U937 cell line was chosen due to its high levels of PLA₂activity, even in the presence of disulfide reducing agents. However,PLA₂ may also be produced by other human cell lines.

The purification procedure is described in detail in Example 1 below.Briefly described, cells were disrupted by N₂ cavitation in a pH 7.5iso-osmotic lysis buffer containing dithiothreitol (DTT),ethylenediaminetetraacetic acid (EDTA) and protease inhibitors. The100,000× g supernatant was purified by elution through the followingorder of chromatographic columns: phenyl, heparin, hydroxyapatite, sizeexclusion and anion exchange chromatography. DTT, a disulfide reducingagent, was added to the elution buffers to inactivate any low molecularweight PLA₂ s. In this manner, selection was directed to purification ofcytosolic PLA₂.

At this point of the purification, the human PLA₂ enzyme preparation ischaracterized by a specific activity of approximately 4 μmols/min/mg inthe mixed micelle assay described in Example 3, below. This specificactivity is comparable to that reported for the intracellular murinePLA₂ by Leslie et al, cited above.

However, when the purified protein was analyzed by SDS-PAGE underreducing conditions, two major proteins were observed with apparentmolecular weights of approximately 60 kD and 110 kD. The smaller proteinwas approximately 4-fold more abundant. Further purification on a sizeexclusion column separated the two proteins, with the activity remainingassociated with the 110 kD protein. No activity was associated with the60 kD protein.

The specific activity of the pure homogeneous material is estimated tobe approximately 20 μmols/min/mg using the mixed micelle assay describedin Example 3 to measure activity, and the intensity of the 110 kD bandon a silver stained SDS-PAGE gel to quantitate protein.

The 110 kD protein was run on a SDS-PAGE gel, the region of the gelcorresponding to 110 kD was excised and subjected to digestion bytrypsin. The tryptic fragments were separated by C-8 reverse phasechromatography and the amino acid sequences were determined for severalfragments. Degenerate oligonucleotides encoding two of these fragmentswere used to screen a cDNA library prepared from the U937 cell line, asdescribed in Example 5.

One complete clone was sequenced. The PLA₂ cDNA sequence from this cloneis shown in Table I below. The DNA sequence of Table I containsapproximately 2247 nucleotides in the proper reading frame to encode aprotein having a calculated molecular weight of approximately 85 kD.

Human PLA₂ according to this invention is characterized by the same orsubstantially the same approximately 749 predicted amino acid proteinsequence (single letter code) encoded by that DNA sequence, asillustrated in Table I below. All tryptic fragments that were sequencedare present in the PLA₂ cDNA sequence and identified by underlining.Those tryptic fragments indicated by asterisks in the Table were used todesign the oligonucleotides. Fragments of the sequence reported in TableI may also retain PLA₂ biological activity.

The cDNA sequence of Table I encodes biologically active human PLA₂,based on detection of the functional polypeptides produced by mammaliancells. The active, recombinantly derived human PLA₂ migrates as anapproximately 110 kD protein on SDS-PAGE, as does the purified enzyme.The cloned sequence of Table I in plasmid PMT-PLA₂ was deposited withthe American Type Culture Collection, 12301 Parklawn Drive, Rockville,Md. on Feb. 27, 1990 under ATCC Accession No. 40759.

                                      TABLE I                                     __________________________________________________________________________     ##STR1##                                                                      ##STR2##                                                                      ##STR3##                                                                      ##STR4##                                                                      ##STR5##                                                                      ##STR6##                                                                      ##STR7##                                                                      ##STR8##                                                                      ##STR9##                                                                      ##STR10##                                                                     ##STR11##                                                                     ##STR12##                                                                     ##STR13##                                                                     ##STR14##                                                                     ##STR15##                                                                     ##STR16##                                                                     ##STR17##                                                                     ##STR18##                                                                     ##STR19##                                                                     ##STR20##                                                                     ##STR21##                                                                     ##STR22##                                                                     ##STR23##                                                                     ##STR24##                                                                     ##STR25##                                                                     ##STR26##                                                                     ##STR27##                                                                     ##STR28##                                                                     ##STR29##                                                                     ##STR30##                                                                     ##STR31##                                                                     ##STR32##                                                                     ##STR33##                                                                     ##STR34##                                                                     ##STR35##                                                                     ##STR36##                                                                     ##STR37##                                                                     ##STR38##                                                                     ##STR39##                                                                     ##STR40##                                                                     ##STR41##                                                                     ##STR42##                                                                     ##STR43##                                                                     ##STR44##                                                                     ##STR45##                                                                     ##STR46##                                                                     ##STR47##                                                                     ##STR48##                                                                     ##STR49##                                                                     ##STR50##                                                                     ##STR51##                                                                     ##STR52##                                                                     ##STR53##                                                                     ##STR54##                                                                     ##STR55##                                                                     ##STR56##                                                                     ##STR57##                                                                     ##STR58##                                                                    __________________________________________________________________________

The nucleotide sequence of this human PLA₂ cDNA of the invention hasbeen compared with the nucleotide sequences recorded in Genbank. Theonly factor with which the human PLA₂ sequence of Table I is believed toshare significant sequence similarity is protein kinase C-gamma (PKC).This sequence similarity may indicate a region of PKC and PLA₂ whichshare a common function. Likely functions include the regulation of thetwo enzymes by calcium and the calcium dependent binding of theseenzymes to membranes.

The second mammalian PLA₂ enzyme of this invention was originallypurified from the murine monocytic cell line RAW 264.7, available fromthe ATCC under accession number TIB71. This factor may also be isolatedfrom other murine cell lines. The methods used to isolate and purify themurine PLA₂ enzyme are analogous to those described above for the humanPLA₂ from U937 cells and are described in detail in Example 2.

Like the human PLA₂ protein described above, the initially purifiedprotein wa analyzed by SDS-PAGE under reducing conditions and two majorproteins were observed having apparent molecular weights ofapproximately 60 kD and 110 kD. Further purification on a size exclusioncolumn as described for human PLA₂ (also as described in Example 2below) indicated that the 60 kD protein was an inactive contaminant andseparated it from the active 110 kD protein. Once again, DTT was used toinactivate any low molecular weight PLA₂ enzymes.

The finally purified, homogeneous, approximately 110 kD murine PLA₂enzyme of this invention is characterized by a specific activity ofapproximately 20 μmols/min/mg in the mixed micelle assay described inExample 3. The intensity of the 110 kD band on a silver stained SDS-PAGEgel was used to quantitate protein. This specific activity is 10-foldhigher than that value observed by Leslie et al, cited above, for the 60kD PLA₂ reportedly obtained from the same cell line. Due to the lowerdegree of purity obtained for the reported smaller molecular weightprotein, it is likely that the 60 kD protein characterized as PLA₂ byLeslie et al is the contaminant of the 110 kD PLA₂ of this inventionand, as such, does not possess PLA₂ activity.

To obtain production of this murine PLA₂ protein by recombinant methods,a sequence from a partial clone of the U937 PLA₂ (from base #877 to the3' end of the sequence of Table I) was used to screen a cDNA libraryprepared from the RAW 264.7 cell line. One positive clone, which wasisolated from a library of 1×10⁶ clones, was partially sequenced. Thepartial sequence of the PLA₂ cDNA from this clone (clone #7) and theassociated predicted amino acid sequence, is shown in Table II below.All or a fragment of this cDNA is believed to encode murine PLA₂ of thisinvention. The sequence determination of this clone is on-going.

The purified RAW 264.7 PLA₂ was also digested into tryptic fragments andsequenced as described for the human PLA₂ enzyme. The sequence of twotryptic fragments (underlined in the sequence of Table II) wereobtained. DNA sequence was available for the first 15 of 18 amino acidsof one of the tryptics, and this sequence is underlined in the table.The sequence for the other tryptic disagreed at two amino acids (markedby asterisks) within the deduced sequence. Based on the partialsequence, the RAW 264.7 enzyme is the murine homologue of the human PLA₂of this invention.

Murine PLA₂ according to this invention is a protein comprising the sameor substantially the same predicted amino acid protein sequence (singleletter code) encoded by the partial cDNA sequence illustrated in TableII below as well as additional sequence. The partial sequence orfragments of the sequence reported in Table II may also retain PLA₂biological activity.

                                      TABLE II                                    __________________________________________________________________________     ##STR59##                                                                     ##STR60##                                                                     ##STR61##                                                                     ##STR62##                                                                     ##STR63##                                                                     ##STR64##                                                                     ##STR65##                                                                     ##STR66##                                                                     ##STR67##                                                                     ##STR68##                                                                     ##STR69##                                                                    __________________________________________________________________________

Allelic variations (naturally-occurring base changes in the speciespopulation which may or may not result in an amino acid change) of theDNA sequences of Table I or Table II, encoding the PLA₂ factorsdescribed above are also included in the present invention, as well asfragments, or derivatives thereof. Thus the present invention alsoencompasses these novel DNA sequences, free of association with DNAsequences encoding other mammalian proteins, and coding on expressionfor novel mammalian PLA₂ polypeptides.

DNA sequences of this invention also include those novel sequences whichhybridize under stringent hybridization conditions [see, T. Maniatis etal, Molecular Cloning (A Laboratory Manual), Cold Spring HarborLaboratory (1982), pages 387 to 389] to the DNA sequence of Table I orTable II. An example of one such stringent hybridization condition ishybridization in 4XSSC at 65° C., followed by a washing in 0.1XSSC at65° C. for thirty minutes. Alternatively an exemplary stringenthybridization condition is in 50% formamide, 4XSSC at 42° C.

DNA sequences, other than those of the known approximately 14 kD PLA₂enzymes of pancreas or non-pancreatic origin, which hybridize to thesequences of Table I or II for human or murine PLA₂ under relaxedhybridization conditions and which code on expression for PLA₂ peptideshaving PLA₂ activity in the mixed micelle assay of Example 3, are alsoincluded in the present invention. Examples of such non-stringenthybridization conditions are 4XSSC at 50° C. or hybridization with30-40% formamide at 42° C. For example, a DNA sequence which sharesregions of significant homology, with the sequences of human or murinePLA₂ of this invention and encodes a protein having one or more PLA₂biological properties clearly encodes a PLA₂ enzyme even if such a DNAsequence would not stringently hybridize to the human PLA₂ sequence ofTable I or the murine PLA₂ sequence of Table II.

Similarly, DNA sequences which code for PLA₂ enzymes of this inventionbut which differ in codon sequence due to the degeneracies of thegenetic code are also encompassed by this invention. Variations in theDNA sequence of PLA₂ which are caused by point mutations or by inducedmodifications of the sequences of Tables I and II, which enhance theactivity, half-life or production of the polypeptides encoded therebyare also encompassed in the invention.

PLA₂ polypeptides may also be produced by known conventional chemicalsynthesis. Methods for constructing the polypeptides of the presentinvention by synthetic means are known to those of skill in the art. Thesynthetically-constructed PLA₂ polypeptide sequences, by virtue ofsharing primary, secondary, or tertiary structural and conformationalcharacteristics with PLA₂ polypeptides may possess PLA₂ biologicalproperties in common therewith. Thus, they may be employed asbiologically active or immunological substitutes for natural, purifiedPLA₂ enzymes in screening of therapeutic compounds and in immunoloqicalprocesses for the development of anti-PLA₂ antibodies.

The PLA₂ enzymes provided herein also include proteins characterized byamino acid sequences similar to those of purified recombinant PLA₂ butinto which modifications are naturally provided or deliberatelyengineered. For example, modifications in the peptide or DNA sequencescan be made by one skilled in the art using known techniques.Modifications of interest in the PLA₂ sequences may include thereplacement, insertion or deletion of a selected amino acid residue inthe coding sequence. For example, one or more of the cysteine residuesmay be deleted or replaced with another amino acid to alter theconformation of the molecule. Mutagenic techniques for such replacement,insertion or deletion are well known to one skilled in the art. [See,e.g., U.S. Pat. No. 4,518,584.]

Other fragments and derivatives of the sequences of human or murine PLA₂which would be expected to retain PLA₂ activity in whole or in part andmay thus be useful for screening or other immunological methodologiesmay also be easily made by one of skill in the art given the disclosuresherein. Such modifications are believed to be encompassed by thisinvention.

The present invention also provides a method for producing the PLA₂proteins of human or murine origin described in Tables I and II. Themethod of the present invention involves culturing a suitable cell orcell line, which has been transformed with a DNA sequence coding onexpression for a PLA₂ polypeptide or an active fragment thereof underthe control of known regulatory sequences. Regulatory sequences includepromoter fragments, terminator fragments and other suitable sequenceswhich direct the expression of the protein in an appropriate host cell.

Suitable cells or cell lines for use in expressing the PLA₂ proteins maybe mammalian cells, such as Chinese hamster ovary cells (CHO), RAT2cells or 3T3 cells. The selection of suitable mammalian host cells andmethods for transformation culture, amplification, screening and productproduction and purification are known in the art. See, e.g., Gething andSambrook, Nature, 293:620-625 (1981), or alternatively, Kaufman et al,Mol. Cell. Biol., 5(7):1750-1759 (1985) or Howley et al, U.S. Pat. No.4,419,446. Other suitable mammalian cell lines, are the monkey COS-1cell line, and the CV-1 cell line. Example 7 describes the expression ofthe human PLA₂ protein in a monkey COS-1 cell expression system. Example10 describes the expression of the human PLA₂ protein in CHO cells.

The novel PLA₂ proteins of this invention can also be convenientlyprepared in invertebrate cells, specifically, in insect cells. Onepresently preferred method for producing this novel composition employsAutographa californica nuclear polyhedrosis virus (AcNPV) as anexpression vector. See, e.g., Miller et al, Genetic Engineering,8:277-298 (Plenum Press 1986) and references cited therein; andprocedures described in published European patent application 155,476].Samples of the extensively studied AcNPV may be obtained from numeroussources, including the Yale Arbovirus Research Unit (YARU) located inNew Haven, Conn. Other viruses known to those skilled in the art may besimilarly employed.

Briefly, a segment of AcNPV DNA encompassing the polyhedrin gene andpromoter is cloned in E. coli using a plasmid vector. The polyhedringene region on the recombinant plasmid DNA is modified by deletion of aportion of the structural gene and insertion of a synthetic polylinkercontaining a band of restriction endonuclease cleavage sites forconvenient insertion into the polyhedrin gene region of the PLA₂ DNAsegment. The PLA₂ DNA attached to a functional polyhedrin promoter andflanked by viral sequences in inserted in a selected enzyme cleavagesite of the plasmid DNA, so that it is under the control of the viralpolyhedrin promoter. This method substantially preserves that portion ofthe polyhedrin gene between the start site of transcription and thestart site of RNA translation, i.e., the segment of the gene encodingthe untranslated portion of the RNA and thus preserves any regulatorysignals contained therein.

The plasmid is then co-transfected with wild-type AcNPV viral DNA intosuitable insect host cells. Thereafter, either by gene conversion orcell-mediated homologous recombination, the DNA from the recombinantplasmid replaces the polyhedrin gene on the full length wild-type AcNPVchromosome. When RNA synthesis occurs during virus infection, the mRNAread from the inserted exogenous DNA directs the expression of the newPLA₂ composition. Specific viruses containing the PLA₂ DNA may beselected for passenger DNA-containing viruses by visually screeningplaques under the light microscope for absence of polyhedrin inclusionbodies (PIBS). Following plaque purification of the recombinant virus,the desired PLA₂ enzyme can be synthesized by cells infected with thisrecombinant virus. Example 8 describes an insect expression system ofinterest for recombinant production of these enzymes.

Bacterial cells may also be useful a host cells suitable for the presentinvention, provided that the molecule produced therein retains activity.For example, the various strains of E. coli (e.g., HB101, MC1061) arewell-known as host cells in the field of biotechnology. Various strainsof B. subtilis, Pseudomonas, other bacilli and the like may also beemployed in this method. Example 9 describes a bacterial expressionsystem of interest for production of these enzymes.

Many strains of yeast cells known to those skilled in the art are alsoavailable as host cells for expression of the polypeptides of thepresent invention. These yeast vectors are constructed employing yeastregulatory sequences to express the cDNA encoding PLA₂ in yeast cells toyield secreted extracellular active PLA₂. [See, e.g., proceduresdescribed in published PCT application WO 86/00639 and European patentapplication EP 123,289.]

The present invention also provides vectors for use in the method ofexpression of novel PLA₂ enzymes. These vectors contain the novel PLA₂DNA sequences which code for PLA₂ polypeptides of the invention. Vectorsincorporating truncated or altered fragments of PLA₂, allelic variantsthereof, or modified sequences as described above are also embodimentsof the present invention and useful in the production of PLA₂polypeptides. The vector employed in the method also contains selectedregulatory sequences in operative association with the DNA codingsequences of the invention and capable of directing the replication andexpression thereof in selected host cells. The vector used in theexamples below is a plasmid designed for expression of heterologousproteins in COS cells. This expression plasmid PMT-PLA₂ described indetail in Example 7.

The novel mammalian PLA₂ enzymes of this invention, purified tohomogeneity from cell sources or produced recombinantly orsynthetically, may be used in novel methods for screening compounds foranti-inflammatory activity, as described in Example 11. For example, aselected compound may be employed in the mixed micelle assay of Example3 with a selected PLA₂ enzyme of this invention. If the normal action ofthe enzyme is inhibited, i.e., the phospholipid is not cleaved torelease the inflammatory mediator precursor, e.g., fatty acid, thecompound demonstrates potential as an inhibitor of inflammatoryreaction.

Similarly the ability of the selected compound may be studied forinhibition of the PLA₂ activity in a liposome assay. An assay systemutilizing natural membranes may also be designed to assess theanti-inflammatory potential of selected compounds. These assays arefurther described in Examples 3 and 11 below.

Alternatively a selected compound may be added to whole cells whichoverexpress the PLA₂ and the cells examined for inhibition of cleavageof the sn-2 acyl bond. For example, both normal cells and cells found tooverexpress the PLA₂ enzyme are cultured in labelled arachidonic acid.Signal is measured between the secreted products of both the normal andoverexpressing cells to provide a baseline of PLA₂ expression. Aselected compound is then added to cultures and the cultures are grownin label arachidonic acid. If there is a difference in the signal (e.g.,the amount of arachidonic acid produced) in the cells in the presence ofthe compound, it inhibited PLA₂ activity and may be a potentialanti-inflammatory compound.

Other uses for these novel PLA₂ enzymes or active fragments thereof arein the development of monoclonal and polyclonal antibodies. Suchantibodies may be generated employing PLA₂, a fragment thereof, or amodified or allelic version thereof as an antigen. By using standardmethods for the development of such antibodies known to one of skill inthe art, polyclonal or monoclonal antibodies are made which may beuseful as research or diagnostic agents to study PLA₂ and inflammatoryfunctions directly.

A pharmaceutical preparation or formulation containing a compoundidentified by the screening method of the present invention to inhibitthe function of PLA₂, may be employed to treat, among other conditions,those disease states characterized by inflammatory reactions, e.g.,rheumatoid arthritis, psoriasis, asthma, inflammatory bowel disease, andother diseases mediated by prostaglandins, leukotrienes or PAF.Therapeutic treatment with compounds identified by the method of thepresent invention may avoid undesirable side effects caused by treatmentwith presently available anti-inflammatory drugs.

Therefore, as another aspect of this invention, methods and compositionsare provided for the treatment of inflammatory conditions. Suchcompositions may comprise a therapeutically effective amount of a PLA₂inhibitor or competitor compound first identified according to thepresent invention in admixture with an optional pharmaceuticallyacceptable carrier. Alternatively the therapeutic compound according tothis invention may contain an antibody to PLA₂ which is capable ofbinding thereto and rendering the enzyme incapable of acting normally.

Pharmaceutical compositions of this invention can be systematicallyadministered parenterally. Alternatively, the composition may beadministered intravenously. If desirable, the composition may beadministered subcutaneously. When systematically administered, thetherapeutic composition for use in this invention is in the form of apyrogen-free, parenterally acceptable aqueous solution. The compositionmay also be made for topical application. The preparation of suchpharmaceutically acceptable protein solutions or formulations, havingdue regard to pH, isotonicity, stability and the like, is within theskill of the art.

The dosage regimen for these compositions involved in a method fortreating the above-described conditions will be determined by theattending physician considering various factors which modify the actionof drugs, e.g. the type of compound employed, the condition, bodyweight, sex and diet of the patient, the severity of any infection, timeof administration and other clinical factors. Progress of the treatedpatient can be monitored by conventional methods.

The following examples illustratively describe the cloning, expressionand production of human PLA₂ and other methods and products of thepresent invention. These examples ar for illustration only and do notlimit the scope of the present invention.

EXAMPLE 1--PURIFICATION OF HUMAN PLA₂

The human monocytic cell line U937 [ATCC CRL 1593] was selected as apotential source for human intracellular PLA₂. Using a humidifiedincubator at 37° C. and 5% CO₂, approximately 10¹¹ U937 cells werecultured in RPMI media supplemented with 10% fetal bovine serum,penicillin (100 units/mL), streptomycin (100 μg/mL) and glutamine (20mM). The cells were harvested by concentration using tangentialfiltration followed by centrifugation. The pelletted cells were twicewashed in ice cold phosphate buffered saline (PBS).

The washed cells were suspended in HEPES (10 mM) lysis buffer at pH7.5containing sucrose (0.34M), EDTA (1 mM), DTT (0.1 mM), ATP (1 mM),leupeptin (1 μg/mL) and freshly added PMSF (1 mM). The cells were lysedby N₂ cavitation at 600-700 psi and the lysate was centrifuged at 50,000g×60 minutes. PLA₂ was purified from the supernatant.

The cleared lysate was adjusted to 0.5M NH₄ SO₄, centrifuged at 50,000g×60 minutes, filtered through a Millipak 60 filter unit, and loadedonto a Toso Haas phenyl-5 PW column (15 cm×21.5 mm) that was previouslyequilibrated with 20 mM Tris HCl buffer (pH7.5) containing 5 mM DTT and0.5M NH₄ SO₄. The PLA₂ activity was eluted at 8 mL/minutes with a 250 mLreverse gradient from 0.5 to 0M NH₄ SO₄ with an extended wash at 0Msalt. The activity eluting at 0M salt was concentrated 10 fold toapproximately 10 mL using an Amicon filtration apparatus with a PM-10filter; 400 μl (pH6.8) MES buffer (1M), 1 mL glycerol and 50 μL DTT (1M)were added; and the solution was passed through a Heparin SepharoseCL-6B column (1 cm×12 cm) equilibrated with 40 mM MES at pH 6.8containing glycerol (10%) and DTT (5mM). Potassium phosphate buffer(pH6.8) and CaCl2 were added to the heparin column eluent to finalconcentrations of 10 mM and 10 μM respectively and the sample was loadedonto a Biogel HPHT column (7.8×100 mm) equilibrated with the same levelsof phosphate buffer and CaCl2.

Fractions (1 mL) were eluted by a linear potassium phosphate gradient(10-500 mM) at a flow rate of 0.4 mL/minute. The activity eluted near140 mM phosphate. The active fractions were concentrated in aCentricon-30 and injected onto a TSK-Gel G3000-SW size exclusion column(60 cm×7.5 mm) which was both equilibrated and run in pH6.5 MES buffer(40 mM) containing KCl (300 mM), DTT (5 mM) and octylglucoside (3 mM).The flow rate was 0.4 mL/minute, and the fraction size was 0.5mL/minute.

The activity eluted at a molecular weight of approximately 100 kD. Thismaterial Was diluted 4 fold with Tris HCl (20 mM) buffer at pH7.5containing glycerol (10%) and DTT (5 mM), loaded onto a Mono-Q HR 5/5column equilibrated with the same buffer and eluted with a 60 mL 0-M KCllinear gradient at a flow rate of 1 mL/minute while collecting 1 mLfractions. The PLA₂ activity eluted in fractions 38-40 at approximately400 mM salt.

When fractions 36-42 were analyzed by SDS-PAGE using Biorad silver stainfor visualization, two major bands were observed with apparent molecularweights of 60 kD and 110 kD with the smaller protein approximately 4fold more abundant.

The resulting partially purified PLA₂ enzyme preparation in Fractions36-42 was examined for activity in the mixed micelle assay, describedbelow. The specific activity of this preparation was found to beapproximately 4 μmols/min/mg.

Fraction 39 was rechromatographed on the G3000=SW size exclusion columnusing 0.25 mL fractions. The 60 kD protein ran as a dimer preceding the110 kD protein. When the 110 kD fraction was removed from the gel andthis purified enzyme material was examined in the mixed micelle assay,the specific activity was found to be approximately 20 μmols/min/mg. The60 kD band was found to be associated with no activity on the sameassay.

EXAMPLE 2--PURIFICATION OF MURINE PLA₂

The murine monocytic cell line RAW 264.7 [ATCC TIB71] was selected as apotential source for murine intracellular PLA₂. Using a humidifiedincubator at 37° C. and 10% CO₂, approximately 10¹⁰ RAW 264.7 cells werecultured in DME media supplemented with 10% fetal bovine serum,penicillin (100 units/mL), streptomycin (100 μg/mL) and glutamine (20mM). The cells were harvested by centrifugation. The pelletted cellswere twice washed in ice cold PBS.

The washed cells were suspended in HEPES (10 mM) lysis buffer at pH7.5containing sucrose (0.34M), EDTA (1 mM), DTT (0.1 mM), glycerol (10%),ATP (1 mM), leupeptin (1 μg/mL) and freshly added PMSF (1 mM). The cellswere lysed by N₂ cavitation at 600-700 psi and the lysate wascentrifuged at 5,000 g×60 minutes. PLA₂ was purified from thesupernatant.

The supernatant was diluted 3 fold with Tris HCl (20 mM) buffer at pH7.5containing glycerol (10%) and DTT (5 mM) to give a protein concentrationof 5 mg/mL, and then one third of this protein solution was loaded ontoa Mono-Q HR 10/10 column equilibrated with the same buffer and elutedwith a 360 mL 0-1M KCl linear gradient at a flow rate of 4 mL/minutewhile collecting 10 mL fractions. The PLA₂ activity eluted atapproximately 400 mM salt. The remaining material was processed in anidentical fashion in two additional runs.

The fractions containing activity were adjusted to 0.5M NH₄ SO₄,centrifuged at 30,000g×20 minutes, and loaded onto a Biorad Phenyl-5 PWcolumn (75 mm×7.5 mm) that was previously equilibrated with 20 mM TrisHCl buffer (pH7.5) containing 5 mM DTT and 0.5M NH₄ SO₄. The PLA₂activity was eluted at 1 mL/minute with a 15 mL reverse gradient from0.5 to 0M NH₄ SO₄ with an extended wash at 0M salt. The activity elutingat 0M salt was diluted 2.5 fold with potassium phosphate buffer (10 mM;pH6.8) containing CaCl2 (10 μM), DTT 5 mM) and glycerol (10%) and wasloaded onto a Biogel HPHT column (7.8×100 mm) equilibrated with the samebuffer.

Protein was eluted into fractions (1 mL) by a linear potassium phosphategradient (10-500 mM) at a flow rate of 0.4 mL/minute. The activityeluted near 130 mM phosphate. The active fractions were concentrated ina Centricon-30 and injected onto a TSK-Gel G3000-SW size exclusioncolumn (60 cm×7.5 mm) which was both equilibrated and eluted with pH6.5MES buffer (40 mM) containing KCl (300 mM), DTT (5 mM) andoctylglucoside (3 mM). The flow rate Was 0.4 mL/minute, and the fractionsize was 0.25 mL/minute.

When this fraction of purified enzyme material was examined in the mixedmicelle assay described below, the specific activity was found to beapproximately 20 μmols/min/mg. The activity eluted at a molecular weightof approximately 100 kD. Fractions from the sizing column were analyzedby SDS-PAGE using Biorad silver stain for visualization to confirm thepurity of the preparation. The activity correlated with a 100 kD band.

EXAMPLE 3--ASSAYS FOR PLA₂ ENZYME ACTIVITY A Mixed Micelle Assay

The currently preferred method of assay for PLA₂ activity is the mixedmicelle assay using 1-palmitoyl 2-[1-¹⁴ C] arachidonoylphosphatidylcholine as substrate and Triton as the micelle formingdetergent. This assay is performed as follows:

1-Palmitoyl 2-[1-¹⁴ C] arachidonoyl phosphatidylcholine (50 nmol;200,000 dpm) is dried under nitrogen and then resuspended in 0.5 mLglycine buffer (80 mM) at pH9.0 containing Triton (200 μM), CaCl₂ (5mM), fatty acid free bovine serum albumin (250 μg/mL) and glycerol(70%). The suspension is sonicated to form mixed micelles ofphospholipid and Triton.

Aliquots of PLA₂ protein solution to be assayed are added to the mixedmicelle solution and incubated at 37° C. in a shaking water bath. Aftera defined time period, the reaction is quenched by the addition of 2.5mL of isopropanol, heptane, and 0.5 M H₂ SO: (800:200:40) with briefvortexing. Heptane (1.5 mL) and water (1.0 mL) are added and thesolution is vortexed for 10 seconds.

The solution separates into an upper phase of heptane, which containsthe [1-¹⁴ C] arachidonic acid liberated by PLA₂, plus a small fractionof unreacted substrate, and a lower isopropanol/aqueous phase whichcontains the bulk of the unreacted substrate. One milliliter of theheptane phase is loaded on a silica column (200 mg) and eluted by ethylether (1 mL). The fatty acid is eluted while the phosphatidyl choline isretained. The eluate is mixed with scintillant and the radioactivitymeasured.

This assay may be performed using various concentrations of thecomponents, alternative phospholipids, different detergents or divalentmetals, and a range of pH.

B. Liposome Assay

For the performance of a liposome assay, the same procedure as describedfor the micelle assay is performed, except detergent is not used. Inthis case, the phospholipid forms a liposome, instead of a mixedmicelle. All the variations mentioned above may increase the sensitivityof the enzyme to inhibitors. This form of the assay may also be employedto detect activity of compounds to inhibit PLA₂.

C. Natural Cell Membrane Assay

As an alternative source of substrate, natural cell membranes may beisolated, and freed of endogenous PLA₂ by EDTA extraction or repeatedfreeze-thaw cycles. The membranes are then added to exogenous PLA₂. Thefree fatty acids resulting from the PLA₂ activity may be detected by gaschromatography.

EXAMPLE 4--PROTEIN SEQUENCE ANALYSIS OF HUMAN PLA₂

Human PLA₂ from fractions 39 and 40 from the Mono-Q HR 5/5 column andthe active fractions from the second sizing column in Example 1 werecombined and run on a 7.5% SDS-PAGE gel. As a reference, a small aliquotof the sample was iodinated with ¹²⁵ I and run out on the gel with therest of the sample. The region of the gel corresponding to molecularweight 110 kD, as determined by autoradiography, was excised anddigested by catalytic amounts of trypsin (2% w/w).

The resulting tryptic peptides were separated by reverse-phasechromatography on a Vydac C-4 column using a linear gradient ofacetonitrile on 0.1% trifluoroacetic acid at 1% acetonitrile per minute.Eluted proteins were monitored by UV absorbance at 214 and 280 nm.

Several peptides were subjected to automated gas phase microsequencing:

(1) G S T M E E E L E N I T T K

(2) I Y E P L D V

(3) M N K

(4) I D P Y V F D

(5) K Y K A p G V P

(6) E A M V E S I E Y

Active fractions from the RAW 264.7 PLA₂ material purified as in Example2 were sequenced in an analogous fashion.

EXAMPLE 5--cDNA LIBRARY CONSTRUCTION AND SCREENING

cDNA libraries are synthesized from polyadenylated RNA from the humanU937 genomic cell line and the RAW 264.7 cell lines, respectively, andcloned into lambda ZAP [Stratagene Cloning Systems, La Jolla, Calif.]essentially as described in J. J. Toole et al, Nature, 312:342-347(1984)] with the following exceptions: the adapters used to blunt-endligate to the double-stranded cDNA have the sequence 5' CTCTAGAGTCCACGG3' and 3' GAGATCTCAGCTGCCTTAA 5'.

For probing the human cDNA, a portion of the tryptic peptide (1) above(amino acid sequence M E E E L E) was used to design a pool of 48-folddegenerate oligonucleotides of 17 bases. An overlapping portion oftryptic (1) above (amino acid sequence E L E N I T) was also used todesign a 140-fold degenerate anti-sense oligonucleotide. The trypticpeptide (5) above (amino acid sequence K Y K A P G) was used to design a96-fold oligonucleotide. The synthetic pools contained all possiblecoding sequences for the listed peptides, and were used to screen300,000 recombinant bacteriophage by the method of K. Jacobs et al,Nature, 313:806-810 (1985).

One human clone, designated clone 38, was shown to hybridize with allthree oligonucleotides. Clone 38 was a partial clone, lacking the codingregion for the amino-terminal 292 amino acids. THis partial clone wasused to screen 1,200,000 recombinant bacteriophage using the protocoldescribed in M. Katan et al, Cell, 54:171-177 (1988). Two bacteriophage,clones 1 and 19 contained approximately 3 kb cDNA inserts which were ofsufficient length to encode a 110 kD protein. The sequence for bothcones were determined for both strands using a Bal31 nuclease deletionseries protocol [Poncz et al., Proc. Nat. Acad. Sci USA, 79:4298-4302(1982)] with subsequent subcloning into appropriate M13 vectors [Messingand Viera, Gene, 19:269-276 (1982)] followed by sequence determinationas described by Sanger et al, Proc. Natl. Acad. Sci. USA, 74:5463-5467(1977). This analysis indicated that clone 19 encodes a protein of85,000 daltons molecular weight that contains all of the trypticpeptides identified by protein sequencing. Clone 1 was identical in thecoding region to clone 19 with the exception of a one base deletion.

Clone 19 is the source of the DNA and predicted amino acid sequence ofTable I above.

EXAMPLE 6--PREPARATION OF RECOMBINANT mPLA₂

Essentially the same procedures described above were employed torecombinant murine PLA₂. A sequence from clone 19 of Table I (from base#877 to the 3' end of the sequence of Table I) was used to screen theRAW 264.7 cDNA library. Clone 7, which was isolated from a library of1×10⁶ clones, was partially sequenced as shown in Table II.

The purified RAW 264.7 PLA₂ was digested into tryptic fragments andsequenced as described for the human PLA₂ enzyme. The sequence of twotryptic fragments were obtained: (6) G T F G D M L D T P D P Y V E and(7) E N E E A E K E Y Q S D N Q A. The sequence for tryptic (7)disagreed at two amino acids within the deduced sequence. Based on thepartial sequence, the RAW 264.7 enzyme is the murine homologue of thehuman PLA₂ of this invention.

Further sequences are selected from this clone to rescreen the libraryto obtain the entire coding region for muPLA₂.

EXAMPLE 7--EXPRESSION OF hPLA₂ IN COS CELLS

To obtain recombinant expression of the hPLA₂ of this invention in COS-1cells, clone 19 from Example 5 above in bluescript was excised by Sal Idigestion, and bluescript was digested with PvuI to enable agarose gelseparation of the 3 kb insert from the 3 kb bluescript. The expressionplasmid PLA₂ -PMT2 was constructed by inserting the excised cDNAencoding PLA₂ into a SalI site that was engineered into the EcoRI siteof the COS expression vector, PMT-2, a beta lactamase derivative ofp91023 [Wong et al, Science, 228:810-815 (1985)]. The plasmid was thentransfected into 2×10⁶ COS cells in a 10 cm dish by the DEAE dextranprotocol [L. M. Sompayrac et al., Proc. Natl. Acad. Sci. USA, 78:7575(1981)] with the addition of a chloroquine treatment [H. Luthman et al,Nucl. Acids Res., 11:1295 (1983)]. The cells are grown in conventionalmedia and the conditioned medium from the transfected COS cells containsPLA₂ enzymatic activity as measured in the mixed micelle assay ofExample 3. Generally cells were harvested 60 hours after the addition ofthe DNA.

The expression of PLA₂ activity in cells transfected with the PLA₂ -PMT2vector was 140-fold greater than in cells transfected with the vectoralone, as determined by the mixed micelle assay.

EXAMPLE 8--INSECT CELL EXPRESSION

To create an insect cell expression system for PLA₂ of the invention,the cDNA sequence of Table I flanked by EcoRI linkers (New Engl. Biolab)is inserted into a polyhedrosis virus expression vector, designatedpEV/55. pEV/55 may be obtained by removing the CSF sequence from theplasmid pEV55-CSF+ harbored in E. coli strain JM101 on deposit at theATCC under No. 40240, by digesting that plasmid with EcoRI. This plasmidis described in D. Miller et al, supra, and contains approximately 3.5kb of viral DNA from the EcoRI fragment of the L-1 variant of theAutographa californica nuclear polyhedrosis virus and a polylinkersequence containing the following endonuclease restriction sites: BglII, XhoI, EcoRI, XbaI, OlaI and KpnI. To allow insertion of the EcoRIfragment of PLA₂ /cDNA, pEV/55 is digested with EcoRI and the PLA₂ /cDNAligated therein. The selected plasmid is designated pEV55-PLA₂.Transformation of E. coli strain JM101 with pEV55-PLA₂ is followed byanalysis of some of the recovered plasmids, both for insertion of thePLA₂ gene and for proper orientation of the insert.

pEV55-PLA₂ is introduced into the insect virus chromosome byco-transfection With Wild-type AcNPV DNA into Spodoptera frugiperdaIPLB-SF21 cell line [J. L. Vaughn et al, In Vitro, 13:213-217 (1977)].Purified Autographa californica NPV DNA and pEV55-PLA₂ DNA areintroduced into Spodoptera frugiperda cells growing on tissue culturedishes by a calcium phosphate transfection procedure [K. N. Potter andL. K. Miller, J. Invertebr. Path., 36:431-432 (1980)]. The jointintroduction of these DNAs into the cells results in a recombinationbetween pEV55-PLA₂ and the viral DNA at the regions of homology betweenthe two; that is, the polyhedrin gene region. Progeny virus from adouble recombination event lose the polyhedrin gene and contain the PLA₂gene under operative control of the polyhedrin promoter.

The progeny virus present in the media over the transfected cells areplaqued onto a fresh monolayer of cells at several different dilutions.The resulting plaques are visually scored and the recombinant virusselected based on the PIB-minus phenotype. A virus which has lost itspolyhedrin gene, as would a virus containing a PLA₂ cDNA inserted at thepolyhedrin encoding locus, will not produce polyhedrin inclusion bodies(PIBs). Plaques that appear PIB-deficient are selected, excised andamplified on fresh cells. The supernatant over these cells is assayedfor PLA₂ activity.

The cell and viral manipulations are performed according to G. D.Pennock et al, Mol. Cell. Biol., 4:399-406 (March 1984). However, thoseof ordinary skill in the art to which this invention pertains willappreciate that other viruses, strains, host cells, promoters andvectors containing the cDNA encoding the amino acid sequence of Table Imay also be used in the practice of this invention. The DNAmanipulations employed in the examples are, unless specifically setforth herein, in accordance with Maniatis et al, cited above.

EXAMPLE 9--EXPRESSION OF PLA2 IN BACTERIA

To produce PLA₂ in bacteria, the cDNA encoding it is transferred into anappropriate expression vector, of which numerous types are known in theart for bacterial expression, using standard molecular biologytechniques. One skilled in the art can manipulate the sequences encodingPLA₂ by eliminating any mammalian regulatory sequences flanking thecoding sequences and inserting bacterial regulatory sequences to createbacterial vectors for expression of PLA₂ by bacterial cells. The cDNAencoding PLA₂ may be further modified to contain different codons tooptimize bacterial expression, as is known in the art.

For example, clone 19 described above in Example 5 in bluescript isexcised by digestion with HgiAI and NsiI to provide a 2.6 kb fragmentencoding PLA₂ of Table I, starting at base 41 and extending 350 baseparis into the 3' untranslated region. This fragment is ligated at theHgiAI site to the following synthetic duplex:

5' TATGTOTTTTATOGATcOTTATcAACATATTATCGTTGAGCA

3' ATACAGAAAATAGCTAGGAATAGTTGTATAATAGCAACTCGT

The 2.6 kb fragment plus the synthetic duplex are then ligated intopAL-981 [ATCC 40134], which is previously digested with Ndel and PstI togive pALPLA₂ -981. This plasmid also contains the amp resistance gene,an aspA terminator, an origin of replication site, the bacteriophage T7ribosome binding site and the bacteriophage lambda pL promoter andbacteriophage lambda transcription terminator.

Plasmid pALPLA₂ -981 is then transformed by conventional techniques intoa suitable bacterial host cell, e.g., an E. coli strain, which containsappropriate elements for controlling the PL promoter for expression ofthe PLA₂ protein. Other bacterial expression systems, such as disclosedin Y. Emori et al, J. Biol. Chem., 264:21885-21890 (1989), may also beconstructed for expression of PLA₂ of this invention.

Bacterially produced PLA₂ is predicted to have a specific activity inthe mixed micelle assay of about approximately 20 μmols/min/mg protein.

EXAMPLE 10--CONSTRUCTION OF CHO CELL LINES EXPRESSING HIGH LEVELS OFPLA₂

One method for producing high levels of the PLA₂ protein of theinvention from mammalian cells involves the construction of cellscontaining multiple copies of the cDNA encoding PLA₂.

The cDNA contains an amplifiable marker, e.g., the DHFR gene for Whichcells containing increasing concentrations of methotrexate (MTX)according to the procedures of Kaufman and Sharp, J. Mol. Biol., (1982)supra. This approach can be employed with a number of different celltypes.

For example, the vector PLA₂ -PMT2 containing the PLA₂ gene in operativeassociation with other plasmid sequences enabling expression thereof inCOS cells, and described and deposited above, contains the PLA₂ codingregion and the DHFR coding region on a single plasmid.

Alternatively, the pALPLA₂ -981 vector described above for bacterialexpression may be employed for co-transfection with a separate plasmidbearing the DHFR gene, such as pAdD26SVpA3 [Kaufman, Proc. Natl. Acad.Sci. USA, 82:689-693 (1985)].

Either the single plasmid bearing both genes or two separate plasmidsare introduced into DHFR-deficient CHO cells, DUKX-BII by calciumphosphate coprecipitation and transfection. DHFR expressingtransformants are selected for growth in alpha media with dialyzed fetalcalf serum. Transformants are checked for expression of PLA₂ bybioassay, immunoassay or RNA blotting and positive pools aresubsequently selected for amplification by growth in increasingconcentrations of MTX (sequential steps in 0.02, 0.2, 1.0 and 5 uM MTX)as described in Kaufman et al., Mol. Cell Biol., 5:1750 (1983). Theamplified lines are cloned, and PLA₂ protein expression is monitored bythe mixed micelle assay. PLA₂ expression is expected to increase withincreasing levels of MTX resistance.

In any of the expression systems described above, the resulting celllines can be further amplified by appropriate drug selection, resultingcell lines recloned and the level of expression assessed using the mixedmicelle assay described in Example 3.

EXAMPLE 11--SCREENING METHOD FOR COMPOUNDS THAT INHIBIT PLA₂ ENZYMEACTIVITY

An exemplary screening technique is described which enables selection ofchemical or pharmaceutical agents having the ability to inhibit PLA₂activity, which employs the PLA₂ enzymes of the present invention. Suchcompounds thereby indicate potential use in controlling the inflammatoryresponse.

For example, the PLA₂ enzyme of Example 5 and a selected compound to bescreen are added to liposomes, mixed micelles, or natural membranesdevoid of endogenous PLA₂ activity, in the assays described in Example3. If the compound is found to inhibit the PLA₂ activity, i.e., renderthe enzyme incapable of cleaving the phospholipid substrate, it haspotential anti-inflammatory activity.

Inhibitors may compete with substrate for the enzyme active site or theymay bind to an allosteric site. Alternatively, the compound may bind tothe phospholipid, or in the case of the natural membranes, anon-phospholipid component of the membrane, and thereby either preventthe enzyme from binding or alter the membrane structure in a fashionthat blocks catalysis. By application of selective labelling ofcomponents of the assays, e.g., the arachidonic acid, the inhibitorycapacity of each selected compound may be measured for further use as ananti-inflammatory agent.

Numerous modifications and variations of the present invention areincluded in the above-identified specification and are expected to beobvious to one of skill in the art. For example, other screeningtechniques may be employed to determine the ability of selectedcompounds to inhibit PLA₂ activity. Such modifications and alterationsto the compositions and processes of the present invention are believedto be encompassed in the scope of the claims appended hereto.

What is claimed is:
 1. A cDNA encoding a human phospholipase A₂ enzymehaving the amino acid sequence set forth in Table I, said DNA sequencebeing selected from the group consisting ofi) a cDNA having the DNAsequence set forth in Table I; ii) a cDNA comprising the SalI insert inplasmid PMT-PLA₂ having accession number ATCC 40759; and iii) a cDNAwhich hybridizes to the cDNA of i) or ii) under stringent conditions andwhich encodes said enzyme.
 2. The cDNA of claim 1, comprises the DNAsequence set forth in Table I.
 3. The cDNA of claim 1, comprises theSalI insert in plasmid PMT-PLA₂ having accession number ATCC
 40759. 4.The cDNA of claim 1, comprises a cDNA which hybridizes to a cDNA havingthe DNA sequence set forth in Table I under stringent conditions andwhich encodes said enzyme.
 5. A cDNA encoding a murine phospholipase A₂enzyme having a partial amino acid sequence as set forth in Table II,said cDNA being characterized by containing the DNA sequence set forthin Table II.
 6. An expression vector containing a cDNA selected from thegroup consisting of the cDNAs of any one of claims 1, 2, 3, 4 and 5,said cDNA being in operative association with a regulatory sequencecapable of directing the replication and expression of said cDNA in ahost cell.
 7. The vector of claim 6, wherein the cDNA is the cDNAcomprising the SalI insert in plasmid PMT-PLA₂ having accession numberATCC
 40759. 8. A cell selected from the group consisting of a mammaliancell, an insect cell, and a bacterial cell, said cell being transformedwith the expression vector of claim
 6. 9. The cell of claim 8, whereinthe cell is a mammalian cell and the expression vector contains the cDNAcomprising the SalI insert in plasmid PMT-PLA₂ having accession numberATCC
 40759. 10. A process for producing a phospholipase A₂ enzyme havingthe amino acid sequence set forth in Table I, which comprises culturinga host cell transformed with a cDNA having the DNA sequence set forth inTable I, said cDNA being in operative association with a regulatorysequence capable of directing the replication and expression of saidcDNA in said cell such that said enzyme is produced and isolated fromculture.
 11. A process for producing a phospholipase A₂ enzyme having apartial amino acid sequence as set forth in Table II, which comprisesculturing a host cell transformed with a cDNA characterized bycontaining the DNA sequence set forth in Table II, said cDNA being inoperative association with a regulatory sequence capable of directingthe replication and expression of said cDNA in said cell such that saidenzyme is produced and isolated from culture.